The invention relates generally to the treatment of tar. Of particular interest to the invention is the purification of tar, especially tar obtained from low-temperature carbonization processes.
When using the newer technologies which have been developed in the area relating to the gasification and combustion of bituminous coal such as, for instance, gasification under pressure and related processes, there are obtained tars which have compositions differing substantially from those of the bituminous coal tars yielded during the coking of bituminous coal.
These tars, that is, the tars derived when using the newer technologies, are also obtained in relatively large quantities from bituminous coal during processes which are carried out at maximum temperatures of 600.degree. to 700.degree. C. For this reason, such tars will also be referred to hereinafter as low-temperature carbonization tars.
An upgrading or purification of low-temperature carbonization tars with the known methods of the coking art, such as those involving decantation of the water and subsequent distillation, is not possible. In particular, the known methods of the coking art cannot be used to upgrade or purify low-temperature carbonization tar by removing impurities such as mineral constituents, ashes, coal particles, coke particles and carbon black particles which are present in solid form. Thus, low-temperature carbonization tars have only a small proportion, that is, about 15 to 30 percent, of distillable constituents whereas the proportion of distillable constituents in the bituminous coal tars obtained from coking plants is between about 45 and 50 percent. Moreover, as a result of the different conditions under which they are formed as opposed to bituminous coal tars, the low-temperature carbonization tars have a high proportion of organic and inorganic impurities as well as a high water content.
Even a combustion of the crude low-temperature carbonization tars cannot be carried out due, in particular, to their high ash contents.